Abstract
Atmospheric particles experience various physical and chemical processes and change their properties during their lifetime. Most studies on atmospheric particles, both in laboratory and field measurements, rely on analyzing an ensemble of particles. Because of different mixing state of individual particles, only average properties can be obtained from studies using ensembles of particles. To better understand the fate and environmental impacts of atmospheric particles, investigations on their properties and processes at a single-particle level are valuable. Among a wealth of analytic techniques, single-particle Raman spectroscopy provides an unambiguous characterization of individual particles under atmospheric pressure in a non-destructive and in-situ manner. This paper comprehensively reviews the application of such a technique in the studies of atmospheric particles, including particle hygroscopicity, phase transition and separation, and solute-water interactions, particle pH, and multiphase reactions. Investigations on enhanced Raman spectroscopy and bioaerosols on a single-particle basis are also reviewed. For each application, we describe the principle and representative examples of studies. Finally, we present our views on future directions on both technique development and further applications of single-particle Raman spectroscopy in studying atmospheric particles.
Highlights
Atmospheric particles or aerosols have considerable effects on climate and human health.(Seinfeld and Pandis, 2016) In general, atmospheric particles can originate from a wide variety of anthropogenic and natural sources
Both partitioning and chemical reactions can change the composition of the particles, altering their properties such as hygroscopicity, cloud condensation nuclei (CCN) activities, phase state, morphology, reactivity, toxicity, and environmental impacts. 49 Physical and chemical processes of atmospheric particles have been examined by numerous experimental approaches: a flowing stream of aerosol particles in an open system, a chamber of suspending particles, a collection of deposited particles, and single particles
The residence time of particles can be extended to a few hours, but other limitations exist, such as long response time to control/change conditions, high cost, and wall loss of particles.(Kang et al, 2007) Deposited particles can be studied using a sample-loaded substrate/filter placed in a flowing-gas reactor or a flow tube with its internal wall coated with particles
Summary
Atmospheric particles experience various physical and chemical processes and change their properties during their lifetime. Because of different mixing state of individual particles, only average properties can be obtained from studies using ensembles of particles. To better understand the fate and environmental impacts of atmospheric particles, investigations on their properties and processes at a single-particle level are valuable. Among a wealth of analytic techniques, single particle Raman spectroscopy provides an unambiguous characterization of individual particles under atmospheric pressure in a non-destructive and in-situ manner. This paper comprehensively reviews the application of such a technique in the studies of atmospheric particles, including particle hygroscopicity, phase transition and separation, and solute-water interactions, particle pH, and multiphase reactions. Investigations on enhanced Raman spectroscopy and bioaerosols on a single-particle basis are reviewed. We present our views on future directions on both technique development and further applications of single-particle Raman spectroscopy in studying atmospheric particles.
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